Method for producing internal member of dry etching chamber

ABSTRACT

A method for producing an internal member of a dry etching chamber by forming an yttria coating on the member. With H 2  gas and Ar gas used as working gases, Ar gas and H 2  gas are supplied to a plasma spray apparatus so the flow-volume ratio of Ar gas to H 2  gas is 6 to 8 with a flow rate of Ar gas set to 60 to 75 liters/min to increase the flow rate of Ar gas with respect to a flow rate of H 2  gas, so that the speed of a plasma jet is increased and the temperature of the plasma jet is decreased, then yttria fine powder having a particle size of 10 to 20 μm is introduced as a powder material to the plasma jet, and the plasma jet containing molten yttria fine powder is sprayed onto the surface of the member.

FIELD

The present invention relates to a method for producing an internal member of a dry etching chamber by forming an yttria coating on the member. (hereinafter sometimes referred to as a chamber internal member of a dry etching chamber or chamber internal member).

BACKGROUND

A dry etching apparatus used in fabricating semiconductor devices fills a chamber with a halogen gas such as chlorine fluoride to generate plasma of the halogen gas in the chamber and etches a surface of a silicon wafer. Chamber internal members, such as an inner wall of the chamber, a gas supply unit, and a shield, are normally made of a metal material such as aluminum or an aluminum alloy. The metal material may be corroded by plasma of the halogen gas.

It has been known to form an yttria coating on the surface of a chamber internal member by thermal spraying in order to prevent corrosion of the chamber internal member, as disclosed in Patent Literature 1. With the method of Patent Literature 1, a sprayed coating with a porosity of 5% to 10% is obtained. Furthermore, paragraph 0018 Patent Literature 1 mentions that it is difficult to produce a sprayed coating having a porosity of 5% or less with atmospheric spraying.

Patent Literature 2 discloses that parts which are exposed to a halogen-based corrosive gas, such as fluorine-based or chlorine-based corrosive gas, or their plasma, is formed of a ceramic sintered body with a surface roughness (Ra) of 1 μm or less and a porosity of 3% or less. The section of Example 1 states that the ceramic sintered body is formed by molding fine metal powder given in Table 1 and sintering the powder at 1300 to 1800° C. Paragraph 0012 of Patent Literature 2 mentions that setting the Ra to 1 μm or less can prevent the concentration of the electric field to suppress the progress of corrosion. Paragraph 0013 of Patent Literature 2 mentions that setting the porosity to 3% or less can prevent deterioration of the surface properties due to corrosion of the porous part, and prevent a reduction in corrosion resistance due to an increase in surface area. Furthermore, while Table 1 shows yttria sintered bodies each having a porosity of 0%, 2%, or 4%, it does not show how to form a coating with such porosity by thermal spraying.

Patent Literature 3 discloses a plasma-resistant member with a surface roughness Ra of 5 μm or less and Rmax of 35 μm or less under the thermally sprayed condition. However, Patent Literature 3 does not disclose that the flow rate of the Ar gas with respect to the flow rate of the H₂ gas at the time of performing thermal spraying.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 3510993

Patent Literature 2: Japanese Patent Publication No. H10-45461

Patent Literature 3: Japanese Unexamined Patent Publication No. 2004-332081

SUMMARY Technical Problem

As mentioned above, it has been known that reducing the porosity and Ra of the surface of the yttria coating improves the corrosion resistance to a halogen gas. However, forming a sprayed coating having a low porosity and an excellent corrosion resistance by thermal spraying has not been implemented yet.

The present invention provides a method for producing an internal member of a dry etching chamber that can form a sprayed coating having high corrosion resistance and low porosity by thermal spraying that can easily be performed.

Solution to Problem

The inventors of the present invention have made extensive studies on formation of sprayed coatings with a low porosity by thermal spraying, and found out that a sprayed coating with a lower porosity and an excellent corrosion resistance are obtained (1) by using a H₂ gas and Ar gas as working gases, and increasing the flow rate of the Ar gas with respect to the flow rate of the H₂ gas to increase the speed of a plasma jet and lower the temperature of the plasma jet, and (2) introducing yttria fine powder with a particle size of 10 to 20 μm to the plasma jet as a powder material. According to the typical yttria spraying method, yttria powder with a particle size of larger than 20 μm and 60 μm or smaller is used. According to the present invention, specifically, fine powder with a particle size of 10 to 20 μm is used as a powder material for plasma spraying. The fine powder with a particle size of 10 to 20 μm is powder with a particle size distribution and a peak lying in the range of not less than 10 μm and not more than 20 μm.

It seems that the use of fine powder with the aforementioned particle size makes denser an yttria coating to be deposited, thereby making it possible to improve the corrosion resistance. However, it has been found through the experiments conducted by the inventors of the present invention that the use of fine powder as a powder material for thermal spraying reduces the corrosion resistance against a halogen gas or the like. This seems to be originated from occurrence of oxygen defects such as Y₂O₂ and Y₂O in yttria (Y₂O₃) caused by overheating the fine powder with a reduced particle size to and above the melting point. Yttria having those oxygen defects cannot exhibit the inherent corrosion resistance at all. With those points in mind, the inventors of the present invention have deliberately increased the supply amount of the Ar gas compared with that in the conventional method with fine powder having a particle size of 10 to 20 μm used as a powder material, and have found that such an increase in the supply amount of the Ar gas densifies the yttria coating, enhancing the corrosion resistance against a halogen gas or the like. This seems to have resulted from the effective prevention of the occurrence of the aforementioned oxygen defects which may be achieved by a reduction in the temperature of the plasma caused by the production of an extra Ar gas that cannot be made into a plasma state due to the increased flow rate of Ar gas.

The present invention provides a method for forming an yttria coating on a member to be used within a dry etching chamber by plasma spraying, including supplying the Ar gas and the H₂ gas serving working gasses to a plasma spray apparatus in such a way that a volume ratio of the Ar gas flow to the H₂ gas flow is 6 to 8 with a flow rate of the Ar gas set to 60 to 75 l/min to increase the flow rate of the Ar gas with respect to a flow rate of the H₂ gas, so that a speed of a plasma jet is increased and a temperature of the plasma jet is decreased, introducing yttria fine powder having a particle size of 10 to 20 μm as a powder material to the plasma jet, and spraying the plasma jet containing molten yttria fine powder onto a surface of the member to form an yttria coating.

In the above production method, the Ar gas and the H₂ gas are supplied to the plasma spray apparatus in such a way that the volume ratio of the Ar gas flow to the H₂ gas flow is 6 to 8. Setting the volume ratio of the Ar gas flow to the H₂ gas flow being within the numerical range allows a dense yttria coating with a high corrosion resistance to be formed on the surface of the internal member of the dry etching chamber.

In the above production method, the flow rate of the Ar gas is set to 60 to 75 l/min. The flow rate of the Ar gas is set within the range and the flow rate of the H₂ gas is set so that a flow-volume ratio of Ar gas to H₂ gas is 6 to 8, thereby forming a dense yttria coating with a high corrosion resistance on the surface of the internal member of the dry etching chamber.

Advantageous Effects of Invention

According to the present invention, a sprayed coating having a low porosity of, for example, 5% or less and a high corrosion resistance and low prosity can be formed on the surface of an internal member of a dry etching chamber by thermal spraying that can easily be performed. The chamber internal member produced by the method of the present invention has a corrosion resistance against a corrosive gas such as the plasma of a halogen gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a plasma spray apparatus.

FIG. 2 is a block diagram of a supply unit for working gases.

FIG. 3 is a block diagram of a supply unit for a powder material.

FIG. 4 is an electron micrograph of yttria coatings of Example 2 and Comparative Example 5.

DESCRIPTION OF EMBODIMENTS

The present invention provides a method for producing an internal member of a dry etching chamber (hereinafter, simply referred to as production method) that forms an yttria coating on a member to be used within a dry etching chamber by plasma spraying. Plasma spraying is performed under reduced pressure or under atmospheric pressure. In the case where plasma spraying is performed under reduced pressure, a dense sprayed coating with few voids can be obtained that provides a high bonding strength between spray particles, and at the interface between the coating and an object to be coated, but it requires decompression equipment. The production method of the present invention can be implemented either under atmospheric pressure or under reduced pressure. The production method of the present invention can easily form an yttria coating sufficiently dense even under atmospheric pressure, so that atmospheric plasma spraying that can easily be performed may preferably be used.

In the production method of the present invention, molten yttria fine powder is sprayed onto an internal member of a dry etching chamber (hereinafter, referred to as chamber internal member) using a plasma spray apparatus. The plasma spray apparatus in use may be a known spray apparatus. FIG. 1 illustrates an example of a plasma spray apparatus used in the present invention.

A plasma spray apparatus 1 of FIG. 1 includes a cathode 11 made of tungsten, an anode 12 made of copper, a working-gas supply unit 13 and a powder-material supply unit 14, and a cooling unit 15. In the plasma spray apparatus 1, an arc is generated between the cathode 11 and the anode 12, and an Ar gas and H₂ gas are supplied there from the working-gas supply unit 13 under a predetermined pressure. The working gas is made into plasma by the arc, and is injected as a plasma jet from a nozzle. Yttria fine powder is extruded from the powder-material supply unit 14 by a feeding gas such as an Ar gas to introduce the powder material into the plasma jet. The introduced powder material is melted by the heat of the plasma jet, and the plasma jet is injected onto the surface of a chamber internal member 21 to form an yttria coating 22 on the surface. Cooling water is passed through a cooling unit 15 to control the temperature of the plasma spray apparatus 1 by heat exchange.

The working-gas supply unit 13 includes a pathway for the Ar gas and a pathway for the H₂ gas as illustrated in FIG. 2. The Ar gas pathway includes an Ar gas tank 31, an electromagnetic valve 33, and a flow meter 34 connected together by a hollow metal pipe or the like in the aforementioned order from the upstream side to the downstream side. Likewise, the H₂ gas pathway includes a H₂ gas tank 35, an electromagnetic valve 37, and a flow meter 38 connected together by a hollow metal pipe or the like in the aforementioned order from the upstream side to the downstream side. Both pathways merge at the downstream of the flow meters 34, 38 to supply a gas mixed at a predetermined ratio to the plasma spray apparatus 1. The flow rates of the Ar gas and H₂ gas may be read from the display of the flow meters 34, 38, so that the flow rates can be regulated by controlling the amount of opening of the electromagnetic valves 33, 37. Since the Ar gas tank 31 and the H₂ tank 35 are respectively filled with the Ar gas and H₂ gas at high pressure, opening the electromagnetic valves 33, 37 causes the Ar gas and H₂ gas to be supplied to the plasma spray apparatus 1 at a predetermined pressure.

As illustrated in FIG. 3, the powder-material supply unit 14 includes an Ar gas tank 41, electromagnetic valves 43, 44, a gas flow meter 45, and a hopper 46 in which a powder material is to be placed, all connected together by a hollow metal pipe or the like in the aforementioned order from the upstream side to the downstream side. The Ar gas supplied through the gas flow meter 45 is supplied toward the hopper 46 to feed the powder material, which is to be extruded from a supply port 461, toward the plasma spray apparatus 1. The hollow pipe is branched at the downstream of the electromagnetic valve 43, and is connected to the hopper 46 via a flow-rate controller 47 and an electromagnetic valve 48. The hollow pipe is further branched at the downstream of the electromagnetic valve 48. The upper passage feeds the Ar gas to the hopper 46 to pressurize inside the hopper 46. The lower passage causes the Ar gas to extrude the powder material to the supply port 461. A pneumatic vibrator 49 is provided below the hopper 46 to generate vibration with air supplied through an electromagnetic valve 50 to support supplying the powder material. An exhaust valve 51 is disposed above the upper portion of the hopper 46. Since the Ar gas tank 41 is filled with the Ar gas at high pressure, opening the electromagnetic valves 43, 44, 48 causes the Ar gas to be supplied to the plasma spray apparatus 1 and the hopper 46 at a predetermined pressure.

In the production method of the present invention, the Ar gas and H₂ gas are used as the working gas, the flow rate of Ar gas is increased with respect to the flow rate of the H₂ gas to increase the speed of the plasma jet and lower the temperature of the plasma jet. Increasing the flow rate of Ar gas with respect to the flow rate of the H₂ gas may be achieved by controlling the amount of opening of the electromagnetic valve 33 in the Ar gas pathway or the electromagnetic valve 37 in the H₂ gas pathway in the working-gas supply unit 13. At the time of increasing the flow rate of Ar gas, the Ar gas and the H₂ gas are supplied to the plasma spray apparatus 1 in such a way that the volume ratio of the Ar gas gas to the H₂ gas is 6 to 8. The volume ratio of the Ar gas flow to the H₂ gas flow falling below the range makes it difficult to obtain a dense yttria coating. This seems to result from the occurrence of oxygen defects which is caused by the overheating of the yttria fine powder due to an excessively increased temperature of the plasma. By contrast, the volume ratio of the Ar gas flow to the H₂ gas flow lying above the range makes it difficult to deposit an yttria coating. This seems to result from an insufficient amount of the H₂ gas which lowers the temperature of the plasma, so that the powder material cannot be melted sufficiently. It is preferable that the power (output) of the plasma spray apparatus be 30 to 45 kW.

In the present invention, yttria fine powder with a particle size of 10 to 20 μm is used as a powder material to increase the flow rate of the Ar gas with respect to the flow rate of the H₂ gas. This makes it possible to obtain a dense and highly corrosion-resistive yttria coating. When the particle size of the powder material falls below the aforementioned range, the powder material in the hopper 46 of the powder-material supply unit 14 aggregates, making it difficult to smoothly supply the powder material. The particle size of the powder material lying above the range makes it difficult to obtain a dense yttria coating.

EXAMPLES

The following gives a more detailed description by way of examples of the present invention.

Yttria coatings were formed on aluminum discs (diameter of 25 mm and a thickness of 9 mm) by atmospheric plasma spraying under the following conditions of Examples 1 and 2, and Comparative Examples 1 to 6. In performing atmospheric plasma spraying, a spray apparatus having the same configuration as the spray apparatus in FIGS. 1 to 3 was used. In Examples 1 and 2, and Comparative Examples 1 to 6, the pressure of the Ar gas was set to 75 Psi, and the pressure of the H₂ gas was set to 50 Psi. The powder material was carried by an Ar gas from the powder material supply unit at a flow rate of 30 g/min. Although the powder material is carried by the Ar gas, the Ar gas is caused to flow to supply the powder material from outside the plasma jet, so that this Ar gas does not affect the plasma jet.

Example 1

A 99.9% purity yttria (Y₂O₃) spray material having a particle size distribution and a peak of the particle size distribution in the range of 10 to 20 μm was used as a powder material. The Ar gas and H₂ gas were used as the working gas, the flow rate of the working gas was adjusted based on the measurements of the flow meters 34, 38 in FIG. 1 in such a way that the flow rate ratio of the Ar gas to the H₂ gas became 7.6, and the atmospheric plasma spraying was performed on the aforementioned aluminum disc. The output of the thermal spray apparatus was set to 32 kW.

Example 2 and Comparative Examples 1 to 6

The flow rate of the Ar gas and the flow rate of H₂ gas were changed as given in Table 1 and the atmospheric plasma spraying was performed on the aforementioned aluminum disc under the same conditions as those of Example 1 except for changes in the flow rate ratio of the Ar gas to the H₂ gas, changes in the power of the plasma spray apparatus as given in Table 1, and changes in the particle size of the powder material as given in Table 1.

Evaluation by visual inspection, measurement of the porosity by the following method, and evaluation of the corrosion resistance by the following method were performed on the aluminum discs that had undergone thermal spraying.

[Measurement of Porosity]

With regard to those of Examples 1 and 2, and Comparative Examples 1 to 6 where an yttria coating was formed, the cross-sectional structure images of the sprayed coatings were imaged by an optical microscope, and image analysis (binarization) was performed on those images to measure the porosity.

[Corrosion Resistance Test]

An inductively coupled plasma (ICP) apparatus was used to perform a corrosion resistance test on those of the aluminum discs of Examples 1 and 2, and Comparative Examples 1 to 6 where an yttria coating was formed. In the test, each of the aluminum discs was set in the associated chamber of the IPC apparatus, plasma was generated while supplying the CF₄ gas and O₂ gas at 0.05 l/min and 0.005 l/min respectively (CF₄:O₂=10:1), and the aluminum discs were exposed to the plasma of the mixed gas for 4 hours. The degree of vacuum was 1.3×10 Pa. After the end of the exposure, the surface shape of each aluminum disc was observed using a laser microscope. In Table 1, “A” is given to an yttria sprayed coating the surface shape of which did not change as apparent from the observation of the surface shapes of the yttria sprayed coatings after the test. In Table 1, “B” is given to an yttria sprayed coating the surface shape of which changed slightly (increase in surface roughness). In Table 1, “C” is given to an yttria sprayed coating the surface shape of which changed significantly (increase in surface roughness). In Table 1, “-” is given to the aluminum discs that were not tested because of formation of no yttria coating.

TABLE 1 Particle Flow rate of size of pow- Supply working gas Flow rate der material of Depo- (l/min) Power ratio of Porosity Corrosion (μm) powder sition Ar H₂ (kW) Ar/H₂ (%) Color resistance Comparative 10 or C C — — — — — — — Example 1 less Comparative 10-20 A A 45 9 32 5.0 4.2 white B Example 2 and black Example 1 10-20 A A 68 9 32 7.6 1.4 white A Example 2 10-20 A A 73 12  33 6.1 1.5 white A Comparative 10-20 A A 68 16  42 4.3 2.5 black C Example 3 Comparative 10-20 A C 80 9 32 8.9 — — — Example 4 Comparative 20-60 A A 45 9 32 5.0 7.8 white C Example 5 Comparative 20-60 A A 68 9 32 7.6 7.0 white C Example 6

Although the aluminum disc of Comparative Example 2 had an appearance showing a mixture of white and black, the aluminum disc had a porosity of 4.2%, and a comparatively favorable result of the corrosion resistance test. The aluminum disc of Example 1 was whitish, had a finely finished appearance, and provided a dense yttria coating with a porosity of 1.4%. The aluminum disc of Example 2 also had a finely finished appearance, and provided a dense yttria coating with a porosity of 1.5%. The aluminum disc of Comparative Example 1 had a difficulty in supplying the powder material from the hopper, and deposition of an yttria coating itself was difficult. The aluminum disc of Comparative Example 3 had a blackish appearance. It is presumed that this appearance has resulted from the overheating of the powder material by an increased plasma temperature due to the excessive supply of the H₂ gas. A dense yttria coating with a porosity of 2.5% was obtained, but the corrosion resistance was insufficient. It is presumed that this result came from the occurrence of oxygen defects in yttria due to the overheating of the powder material. An yttria coating could not be formed on the aluminum disc of Comparative Example 4. It is presumed that this result came from a reduction in plasma temperature due to the excessive supply of the Ar gas so that the powder material was not melted sufficiently to form a coating. The aluminum discs of Comparative Examples 5 and 6 provided whitish yttria coatings, but the porosity was high so that yttria coatings were not dense. It is presumed that this result came from the large particle sizes of the powder material, which provided coarse yttria coatings and did not provide sufficient corrosion resistance.

For the yttria coatings formed by the methods of Example 1 and Comparative Example 6, photographs taken with a scanning electron microscope (SEM) are shown in FIG. 4. In FIG. 4, the upper side shows the images of the coating surfaces, and the lower side shows the images of the cross sections of the coatings. As apparent from the comparison of the cross sections, the production method of the present invention can easily form a dense yttria coating by plasma spraying.

REFERENCE SIGNS LIST

1 Plasma spray apparatus

11 Cathode

12 Anode

13 Working-gas supply unit

14 Powder-material supply unit

15 Cooling unit

16 Insulator

21 Chamber internal member

22 Yttria coating

461 Supply port 

1. A method for forming an yttria coating on a member to be used within a dry etching chamber by plasma spraying, the method comprising: supplying Ar gas and H₂ gas as working gases to a plasma spray apparatus in such a way that a volume ratio of the Ar gas flow to the H₂ gas flow is 6 to 8 with a flow rate of the Ar gas set to 60 to 75 liters/minute to increase the flow rate of the Ar gas with respect to a flow rate of the H₂ gas, so that a speed of a plasma jet is increased and a temperature of the plasma jet is decreased; introducing yttria fine powder having a particle size of 10 to 20 μm as a powder material to the plasma jet; and spraying the plasma jet containing molten yttria fine powder onto a surface of the member to form an yttria coating. 